Current supply apparatus



P 11, 1951 F. w. ANDERSON 2,567,797

' CURRENT SUPPLY APPARATUS Filed Feb. 18, 1950 ELOAD INVEN TOR y F. n.ANDERSON A TTOPNEY Patented Sept. 11, 1951 CURRENT SUPPLY APPARATUSFrederic W. Anderson, Lynbrook, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication February 18, 1950, Serial No. 144,964

1 Claim. 1

This invention relates to current supply apparatus and more particularlyto a full wave phase shift bridge circuit for controlling the currentsupplied by a space current rectifier to a load.

An object of the invention is to provide improved apparatus for shiftingthe phase of an alternating voltage.

This invention is an improvement over the invention disclosed andclaimed in my copending application Serial No. 111,208, filed August 8,1949.

In a preferred embodiment of the invention, herein shown and describedfor the purpose of illustration, there is provided a full wave rectifiercircuit comprising two gas-filled, grid controlled, space dischargetubes, known as thyratrons, for rectifying current from analternating-current supply source and for supplying the rectifiedcurrent to a load. There is derived from the output of a full wave phaseshift bridge circuit to which current is supplied from the supplysource, an alternating voltage of variable phase which is impressed uponthe grid-cathode circuits of the rectifier tubes for initiating spacecurrent conduction in the tubes alternately, each tube being madeconductive during a variable portion of each half cycle of thealternating voltage in which its anode is positive with respect to itscathode as determined by the phase of the derived voltage relative tothat of the supply source.

The full wave phase shift bridge circuit comprises four impedance arms,two similar arms of which are half portions, respectively, of asecondary winding of a transformer the primary winding of which isconnected to the alternating current supply line. A third bridge arm isa capacitance and the fourth bridge arm comprises the space currentpaths of two grid controlled space current devices or triodes havingtheir space current paths reversely connected in parallel, that is, theanode of a first of the devices being connected to the cathode of thesecond device and the cathode of the first device being connected to theanode of the second device. A shunt current path connected across theanode-cathode paths of the two space current devices comprises When thepolarity across the first of the triodes is such as to cause spacecurrent to flow therein, the current fiow through the first of thevaristors which is in a circuit connecting the anode and control grid ofthe first triode is in the reverse or high resistance direction and thecurrent flow through the second varistor which is in a circuitconnecting the control grid and cathode of the first triode is in theforward or low resistance direction. The voltage drop across the secondvaristor is thus negligibly small and the anodecathode resistance of thetriode is determined solely by the negative control potential impressedupon its grid with respect to its cathode. A similar operation resultswhen the second triode conducts space current since the current flowthrough the second varistor is then in the reverse or high resistancedirection and that through the first varistor is in the forward or lowresistance direction so that the voltage drop across the first varistoris negligibly small.

The single figure of the accompanying drawing is a schematic view of aregulated rectifier embodying the invention.

two oppositely poled asymmetrically conducting devices such asvaristors. The common terminal of the varistors is connected to the gridof each triode through a source of variable, unidirectional controlvoltage which may vary in accordance with changes of load voltage orload current, for example, the positive terminal of the control voltagesource being connected to the common terminal of the varistors;

Referring to the drawing, there is shown a full wave rectifiercomprising two gas-filled, grid controlled, space current tubes l0 andII for rectifying current supplied thereto from an alternatingcurrentsupply source l2 through a circuit comprising a transformer I 3 and forsupplying rectified current to a load circuit comprising a ripple filterhaving a series inductance element I4 and a shunt condenser I 5, and aload l1. One end terminal of the secondary winding of transformer I3 isconnected through inductance winding l8 and inductance element I9 to theanode of tube l0 while the other end terminal of the secondarytransformer winding is connected through inductance winding 20 andinductance element 2| to the anode of tube H, windings l8 and 20 havinga common core. Filtering condenser 22 is provided in a path connecting acommon terminal of inductance windings I8 and I9 and a common terminalof inductance windings 20 and 2|. Filtering condenser 23 is in a pathconnecting the common terminal of windings l8 and I9 and the cathode oftube I0 while condenser 24 is in a path connecting the common terminalof windings 20 and 2| and the cathode of tube H.

The instant at which conduction is initiated in tubes [0 and II duringthe half cycle periods of alternating-current source I! when the anodesof tubes l0 and II, respectively, are positive with respect to theircathodes is controlled by varying the phase of the alternating voltagesderived from source I! and impressed upon the control gridcathodecircuits of tubes l and I I through input transformer 25. 'One endterminal of the secondary winding of transformer 25 is connected througha resistor 26 to the grid of tube Hi, the other end terminal of thesecondary winding is connected through a resistor 21 to the grid of tube,H and a mid-tap of the secondary winding is connected to the cathodesof tubes In and II. A condenser 28 is connected across one half portionand condenser 29 is connected across the other half portion of thesecondary winding oi transformer 25.

The primary of transformer 25 is connected to the output vertices of aphase shift bridge network 30 having four impedance arms. An alternatingvoltage derived from alternating-current source I2 is impressed acrossthe input vertices of the bridge by means of a transformer 3| theprimary of which is connected to the current source l2. One half portionof the secondary winding of transformer 3| is connected in one arm ofthe bridge, the other half portion of the secondary winding is connectedin a second arm of the bridge and a condenser 32 is connected in a thirdarm. The fourth arm of the bridge network has three parallel branchpaths, the first path comprising the space current path of a triodespace current device 33, the second branch path comprising the spacecurrent path of a second triode 34 and the third branch path comprisingasymmetrically conducting varistors 35 and 36 having a common terminal31. asymmetrically conducting varistor may be a copper oxide or seleniumrectifying element, for example, the resistance of which in the forwardor conducting direction is much less than its resistance in the reversedirection. The characteristics of such elements are described, forexample, in an article by J. A. Becker on page 322 of "Bell LaboratoriesRecord, for July 1940. Triode 33 comprises an anode 40, control grid 4|and cathode 42 while triode 34 comprises an anode 43, control grid 44and cathode 45. Anode 40,'catliode 45, a terminal of varistor 35 and aterminal of condenser 32 are conductively connected to one of the outputvertices of the bridge network. Cathode 42, anode 43 and a terminal ofvaristor I 36 are conductively connected to one of the input vertices ofthe bridge. During half cycle periods of the alternating current whenanode 40 is at a positive potential with respect to the potential ofcathode 42, current flows through varistor 35 in the reverse or highresistance direction and through varistor 36 in the forward or lowresistance direction with the result that the voltage drop acrossvaristor 36 is negligibly small. During half cycle periods of oppositepolarity when anode 43 is positive-with respect to cathode 45, currentflows through varistor 36 in the reverse or high resistance directionand through varistor 35 in the forward or low resistance direction withthe result that the voltage drop across varistor 35 is negligibly small.The triodes 33 and 34 are preferably the triodes of a twin triode tubebut two single triode tubes can be provided if desired.

A voltage divider comprising resistors 50 and in series, is connectedacross the load II. There is provided an amplifier space current device52 to which space current is supplied by rectifier In, H through acircuit which may be traced from the positive load terminal, throughresistors 50 .and 53 to the anode, and from the cathode of tube 52 tothe negative load terminal.

The control grid-cathode circuit of tube 52 may be traced from the grid,through resistor 54 to the negative terminal of battery 55 and from thepositive battery terminal, through resistor 5| to the cathode of tube52. Instead of the battery 55 for providing a reference voltage sourcein the grid-cathode circuit of tube 52, there may be used a portion atleast of the voltage across a cold cathode gas-filled tube to whichrectified current is supplied through a resistive circuit. One plate ofa condenser 56 is connected to the control grid of tube 52 and the othercondenser plate is connected to the cathode of the tube. Resistor 54 andcondenser 56 are provided for preventing hunting.

The amplifier circuitcomprising tube 52 causes to be produced acrossresistor 53 a unidirectional voltage having amplitude changescorresponding to load voltage changes, the percentage change of thevoltage across resistor 53 being large relative to the percentage changeof the load voltage. When the load voltage increases by a small amount,for example, the voltage across resistor 53 increases to make the grid4i more negative with respect to cathode 42 and to make the grid 44 morenegative with respect to cathode 45. The resistance of the arm of thebridge comprising the space current paths of triodes 33 and 34 is thusincreased during both half cycles of the alternating-current wave toshift the phase, in the lagging direction, of the voltage wave appliedto the grid-cathode circuits of tubes Ill and H with respect to thevoltage applied to the anode-cathode circuits of the tubes. Spacecurrent conduction in tubes Ill and H is thus initiated later in thepositive half cycles of the anode voltage to cause the initially assumedincrease of load voltage to be minimized. Instead of connecting theleads 51 and 58 across resistor 5|, they may be connected across a smallresistor which is in series with the load for causing the load currentto be maintained substantially constant.- Moreover, if desired, avoltage proportional to the load voltage and a voltage proportional tothe load current may be combined to set up a voltage equal to the sum orthe difference of the two voltages which may be impressed across theleads 5! and 58.

What is claimed is:

In combination, a full wave rectifier comprising two space currentrectifying devices each having an anode, a cathode and a control gridfor rectifying current from an alternating-current supply source and forsupplying the rectified current to, a load circuit, a phase shift bridgenetwork'having four impedance arms for shifting the phase of analternating voltage supplied from said supply source to the inputvertices of said bridge, means for supplying said phase shifted wavefrom the output vertices of said bridge to the grid-cathode circuits ofsaid rectifying devices to control the rectified current supplied fromsaid rectifier to said load, a first of said impedance arms comprising afirst condenser, a second of said impedance arms comprising a thirdspace current device having an anode'connected to one of said outputvertices, a cathode connected to one of said input vertices and acontrol grid, a fourth space current device having an anode connected tosaid one input vertex, a cathode connected to said one output vertex anda control grid, a first asymmetrically conducting varistor connectedbetween said one output vertex and a common terminal and presenting itsrelatively high reverse resistance to ourrent flow therethrough in adirection from said one output vertex to said common terminal, a secondasymmetrically conducting varistor connected between said one inputvertex and said common terminal and presenting its relatively highreverse resistance to current flow therethrough in a direction from saidone input terminal to said common terminal, a firth space current devicehaving an anode, a cathode and a control electrode, means for connectingthe anode of said fifth space current device to the control electrodesof said third and fourth space current devices, a first resistor, meansfor connecting the terminals of said first resistor to said commonterminal and to the anode of said fifth space current device,respectively, means for impressing a portion at least of the loadvoltage across a current path comprising in series said first resistorand the space current path of said fltth space current device, a secondresistor, an auxiliary source of unidirectional voltage, a

circuit connecting said control electrode and said cathode of said fifthspace current device comprising in series said second resistor, saidauxiliary voltage source and in opposition to said auxiliary source aportion at least of said load voltage, a second condenser, and means forconnecting the terminals of said second condenser to the controlelectrode and cathode, respectively, oi said mm space current device.

FREDERIC W. ANDERSON.

REFERENCES CITED The following references are of record in the 15 fileof this patent:

UNITED STATES PA'I'ENTS Number Name Date 2,141,922 Lord Dec. 27. 1938 202,196,680 Milarta Apr. 9. 1940 2,329,127 Levy Sept. 7, 1943

